1. Field of the Invention
The instant invention relates to a new method of detecting the carbon monoxide concentration of a gas. More particularly, the instant invention relates to a new method of detecting the carbon monoxide concentration of a gas by using a resistance gas sensor which consists of a forked base from which a pair of arms extend, a resistance layer formed on said forked base, and a catalyst layer formed on one of said pair of arms.
Said gas containing carbon monoxide may be exhaust gas from a car engine or the like. An exhaust gas recirculating system (EGR system) in which a portion of the exhaust gas of the engine is recirculated to the intake side of the engine is a preferable system for decreasing the concentration of nitrogen oxide contained in a exhaust gas of the engine, especially the diesel engine. Nevertheless, the combustion of the intake gas in the engine may be incomplete if the recirculating volume of the exhaust gas, (i.e., the EGR ratio) becomes excessive. In this case, carbon monoxide concentration, smoke quantity, and the like in the exhaust gas may increase. Therefore it is preferable to detect the carbon monoxide concentration of the exhaust gas and to control the EGR ratio by this result.
2. Description of the Prior Art
Hitherto resistance gas sensors have been used to detect carbon monoxide. Such resistance gas sensors consist of a forked base from which a pair of arms extend. One of the arms is for reference, and the other arm is for detection. A linear resistance layer is formed on the surface of the forked base, a linear heating layer is formed on the backface and/or on the inside of the forked base, and a catalyst layer is formed on the surface of the arm used for detection.
In such a resistance gas sensor, the change of the resistance value is output. The change of the resistance value originates in the reaction heat of oxidation of carbon monoxide contained in the exhaust gas. Such oxidation may be caused to occur by contacting the exhaust gas with the catalyst layer of the resistance gas sensor. Carbon monoxide concentration is calculated from the output change of the resistance value. In such oxidation, free energy of activation may be supplied to the reaction by heating the heating layer of the resistance gas sensor. Nevertheless, as above mentioned, the heating layer is independent of the resistance layer in the traditional resistance gas sensor, so it is necessary to arrange a terminal for outputting from the resistance layer and a separate terminal for inputting to the heating layer. Therefore, in the prior art, separate processes are necessary to form the heating layer and the resistance layer, and separate terminals are necessary to output from the resistance layer and to input to the heating layer. The above mentioned complexities in the manufacturing process and in the structure may be a large disadvantage, especially for small resistance gas sensors for car use.